feat(loyalty): remind customers before balances expire

Adds what the customer sees of expiry (docs/prd-point-coin.md F6, F12,
PC-504).

GET /customer/wallet/expiring lists everything that will expire, per
currency and day, soonest first. GET /customer/wallet already had the
nearest expiry per currency.

The expiry job now also sends reminders, with the settings of note N4 as
decided: once, reminder_days before (7 by default, 0 for none), per
currency. A customer gets one FCM push per currency and expiry day,
however many lots make it up: "150 EnakPoint akan kedaluwarsa pada 31 Okt
2026. Pakai sebelum hangus.", with type WALLET_EXPIRING, the currency,
amount and expiry_date in its data. Reminders cover whatever falls within
the window, so a run that was missed catches up rather than skipping a day.

Migration 000097 adds wallet_expiry_reminders, one row per customer,
currency and expiry day. The row is written before the push is sent, so
several instances of the job or a restart never remind twice; a push that
then fails is logged and not retried. Lots that expire later on the same
day as an earlier reminder are not reminded of again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/models/wallet.go

@@ -157,3 +157,10 @@ type PointPaymentPreview struct {
 	// Rupiah covered by MaxPoints.
 	MaxAmount int64 `json:"max_amount"`
 }
+
+// CustomerWalletExpiringList is GET /customer/wallet/expiring (docs/prd-point-coin.md
+// F6): everything that will expire, per currency and day, soonest first.
+type CustomerWalletExpiringList struct {
+	Point []CustomerWalletExpiring `json:"point"`
+	Coin  []CustomerWalletExpiring `json:"coin"`
+}